Sugar beet is a highly salt-tolerant crop. However, its ability to withstand high salinity is reduced compared to sea beet, a wild ancestor of all beet crops. The aim of this study was to investigate transcriptional patterns associated with physiological, cytological and biochemical mechanisms involved in salt response in these closely related subspecies. Salt acclimation strategies were assessed in plants subjected to either gradually increasing salt levels (salt-stress) or in excised leaves, exposed instantly to salinity (salt-shock). The majority of DEGs was down-regulated under stress, which may lead to certain aspects of metabolism being reduced in this treatment, as exemplified by lowered transpiration and photosynthesis. This effect was more pronounced in sugar beet. Additionally, sugar beet, but not sea beet, growth was restricted. Silencing of genes encoding numerous transcription factors and signaling proteins was observed, concomitantly with the up-regulation of lipid transfer protein-encoding genes and those coding for NRTs. Bark storage protein genes were up-regulated in sugar beet to the level observed in unstressed sea beet. Osmotic adjustment, manifested by increased water and proline content, occurred in salt-shocked leaves of both genotypes, due to the concerted activation of genes encoding aquaporins, ion channels and osmoprotectants synthesizing enzymes. bHLH137 was the only TF-encoding gene induced by salt in a dose-dependent manner irrespective of the mode of salt treatment. Moreover, the incidence of bHLH-binding motives in promoter regions of salinity-regulated genes was significantly greater than in non-regulated ones. Maintaining homeostasis under salt stress requires deeper transcriptomic changes in the sugar beet than in the sea beet. In both genotypes salt shock elicits greater transcriptomic changes than stress and it results in greater number of up-regulated genes compared to the latter. NRTs and bark storage protein may play a yet undefined role in salt stress-acclimation in beet. bHLH is a putative regulator of salt response in beet leaves and a promising candidate for further studies.

Last finding indicates that post-transcriptional processes are significant in low-oxygen conditions, but their nature is poorly understood. Here, we localized poly(A) RNA and mRNA coding proteins involved and not involved with resistance to hypoxia in Lupinus luteus and Arabidopsis thaliana during submergence and after recovery of aerobic conditions. We showed a strong nuclear accumulation of poly(A) RNA and 6 of 7 studied mRNAs with a concurrent strong reduction in RNA polymerase II transcription during hypoxia. In this study, the nucleus did not accumulate mRNA of the ADH1 (alcohol dehydrogenase 1) gene, which is a core hypoxia gene. The RNA accumulation in the nucleus is among the mechanisms of post-transcriptional gene regulation that prevents translation. However re-aeration was accompanied by a strong increase in the amount of the mRNAs in the cytoplasm and a simultaneous decrease in nuclear mRNAs. This finding indicates that the nucleus is a storage site for those of mRNAs which are not involved in the response to hypoxia for use by the plants after the hypoxic stress. In this study, the highest intensity of RNA accumulation occurred in Cajal bodies (CBs); the intensity of accumulation was inversely correlated with transcription. Under hypoxia, ncb-1 mutants of Arabidopsis thaliana with a complete absence of CBs died sooner than wild type (WT), accompanied by a strong reduction in the level of poly(A) RNA in the nucleus. These results suggest that the CBs not only participate in the storage of the nuclear RNA, but they also could take part in its stabilization under low-oxygen conditions.